A steam turbine includes a rotor which rotates about an axis and a casing which covers the rotor. The rotor includes a rotor shaft which extends in an axial direction about an axis and a plurality of stages of rotor blade rows which are fixed to an outer periphery of the rotor shaft and are arranged in the axial direction. The steam turbine includes a stator vane row which is fixed to an inner periphery of the casing and is disposed on an upstream side of each stage of the plurality of stages of rotor blade rows.
In each of a plurality of rotor blade configuring the rotor blade row of each stage, a blade root of the rotor blade is embedded into an outer peripheral portion of a disk portion which extends from a shaft core portion of the rotor shaft toward a radially outer side.
In the rotor blade row of each stage, a pressure difference is generated between an upstream side and a downstream side thereof. A large force acts on the rotor in an axial direction (thrust direction) of the rotor by this pressure difference. Accordingly, a balance hole which communicates with the upstream side and the downstream side of the rotor blade row is formed in the disk portion, and thus, the pressure difference between the upstream side and the downstream side of the rotor blade row decreases, and the force in the thrust direction decreases.
Patent Document 1 discloses a configuration in which a gap is formed between a bottom portion of a blade groove fitted into a blade root of each rotor blade formed in a disk portion and the blade root of the rotor blade and this gap functions as a balance hole.